Most are set-up to switch to propane when not connected to electrical "shore" power. Most seem to have an automatic setting that accomplishes this, but some may not. Make sure the propane tank being used is on and if a two tank system, make sure the valve between the two tanks is either set to draw from the full tank or in the middle which will automatically draw from the full tank. Next check your refrigerator settings, if there is an automatic selection make sure it is on auto, then plug the RV in to electrical power turn the refrigerator and verify it is running. If it is, unplug the electrical cord and watch to see if it switches over to propane. If there is no auto selection, set it manually to propane, then do the above. If the above does not work and your propane stove and heater work, then there would appear to be a problem with your refrigerator, specifically the switching mechanism or the propane supply connection to the refrigerator.